In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and/or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5–20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.

Shear strength and stiffness of silty sand

This paper describes recent advances in stability analysis that combine the limit theorems of classical plasticity with finite elements to give rigorous upper and lower bounds on the failure load. These methods, known as finite-element limit analysis, do not require assumptions to be made about the mode of failure, and use only simple strength parameters that are familiar to geotechnical engineers. The bounding properties of the solutions are invaluable in practice, and enable accurate limit loads to be obtained through the use of an exact error estimate and automatic adaptive meshing procedures. The methods are very general, and can deal with heterogeneous soil profiles, anisotropic strength characteristics, fissured soils, discontinuities, complicated boundary conditions, and complex loading in both two and three dimensions. A new development, which incorporates pore water pressures in finite-element limit analysis, is also described. Following a brief outline of the new techniques, stability solutions ...

Geotechnical stability analysis

Scientific approaches to pile design have advanced enormously in recent decades and yet, still, the most fundamental aspect of pile design—that of estimating the axial capacity—relies heavily upon empirical correlations. Improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile, but quantification of the changes in stress and fabric is not straightforward. This paper addresses the degree of confidence we can now place (a) on the conceptual and analytical frameworks for estimating pile capacity, and (b) on the quantitative parameters required to achieve a design. The discussion is restricted to driven piles in clays and siliceous sands, with particular attention given to extrapolating from design approaches derived for closed-ended piles of relatively small diameter to the large-diameter open-ended piles that are used routinely in the offshore industry. From a practical viewpoint, we need design approaches that minimise sensitivity...

Science and empiricism in pile foundation design

Tire shreds and tire shred  soil mixtures can be used as alternative backfill material in many geotechnical applications. The reuse of tire shreds may not only address growing environmental and ec...

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Behaviour of tire shred - sand mixtures

Closure to “Determination of Bearing Capacity of Open-Ended Piles in Sand” by Kyuho Paik and Rodrigo Salgado

Closure to “Load Testing of a Closed-Ended Pipe Pile Driven in Multilayered Soil” by Daehyeon Kim, Adriano Virgilio Damiani Bica, Rodrigo Salgado, Monica Prezzi, and Wonje Lee

Pile foundations have been used in construction for thousands of years but only in the last few decades has there been significant progress in the technology of pile installation. This progress on construction has not been matched by progress in the analysis and design of these foundation elements, which has lagged considerably. This is in large part due to considerable difficulties in analyzing both pile installation and the response of piles to various types of loadings rigorously. Given these difficulties, the profession has in general relied heavily on empiricism and relatively crude design approaches. This may well change due to pressures from different directions, particularly the progress in code design (the push towards load and resistance factor design in geotechnical engineering requires a much better grip on all the factors that need to be considered in calculating pile resistances and on the uncertainties in quantities and analyses, requiring sounder analytical frameworks) and economics (materials costs have been rising from multi-decade lows a few years back, a trend that would make it more economically interesting to have optimal designs). In this paper, the authors examine the design process for axially-loaded non-displacement piles with a focus on assessing the strength of the recently developed analyses. The authors show that, for these types of piles, design can be placed on a strong theoretical basis and discuss the implications for the future.

The Axial Resistance of Nondisplacement Piles

Determining the shape of the slip surface is an important step in the calculation of earth pressure on a retaining wall. Fundamental assumptions are made regarding the geometry of shear bands and slip surfaces in methods that are widely used in the analysis and design of retaining walls. Experimental visualization allows observation not only of how the slip surface develops but also how it evolves with wall movement and soil deformation. This paper presents results of experiments performed to study the formation of shear bands in sand retained by a flexible wall. Particular attention was paid to the effect of the initial sand density on the distribution of volumetric and maximum shear strains as a function of wall displacement. To achieve these goals, a small-scale test box was built to model a plane-strain condition for a retaining wall system. A model flexible wall was hinged to the bottom face of the test box. The wall was then backfilled with silica sand using the air pluviation method. The pluviator openings were such that different relative densities were achieved (Dr=15% and 77%). A displacement controlled mechanism was employed to apply outward displacement on the crest of the wall away from the backfill material to model an active-pressure mode of failure. The Digital Image Correlation (DIC) technique was used to observe shear band evolution with progressive outward movement of the wall. The results highlighted the suitability of this technique to visualize and characterize the formation of slip surfaces in laboratory-scale experiments.

Rodrigo Salgado

Papers

Closure to “Determination of Bearing Capacity of Open-Ended Piles in Sand” by Kyuho Paik and Rodrigo Salgado

Closure to “Load Testing of a Closed-Ended Pipe Pile Driven in Multilayered Soil” by Daehyeon Kim, Adriano Virgilio Damiani Bica, Rodrigo Salgado, Monica Prezzi, and Wonje Lee

The Axial Resistance of Nondisplacement Piles

Visualization of Active Mode of Failure behind Flexible Walls under Pure Rotation Using Digital Image Correlation

The Axial Capacity of Closed-Ended Pipe Piles Driven in Gravelly Sands